The present invention relates to a highly advantageous method of fabricating a semiconductor device so that the contact pads on an integrated circuit substrate within the device can be readily and reliably connected to predetermined regions of a semiconductor wafer mounted to the substrate. Although the invention is disclosed in the context of an IR/CCD focal plane structure, it is not limited to such devices.
U.S. Pat. No. 4,196,508, which is incorporated by reference herein, discloses fabrication of hybrid mosaic IR/CCD focal plane structures on a silicon substrate containing integrated circuit CCD signal processing circuitry. Each structure includes photodetectors which are interconnected to the signal processing circuitry with thin film electrical interconnects and contact pads.
Methods disclosed in the patent for obtaining access to the contact pads in order to make the thin film electrical interconnects have proven to be methods requiring a relatively high degree of skill and resulting in a relatively low yield of useable devices. In addition, the disclosed methods are primarily applicable to devices having a relatively low density of detectors, a typical device having 32 detectors coupled to 32 contact pads. This is in contrast to present interest in much higher density devices such as those including 1000 or more detectors, each individually coupled to its own contact pad.
Accordingly, the present invention provides for more readily and reliably obtaining high quality thin film electrical interconnects through processes compatible with relatively high volume production. As such, the present invention permits fabrication of devices which have much higher detector element packing densities than previously obtainable. At the same time, the present invention reduces the level of processing skill required and increases the yield of high quality devices.